The mechanisms of ion transport through lipid bilayer will be studied with emphasis on ion transport through and ion-specificity of, polypeptide channels incorporated into the bilayer matrix. The mechanism(s) of ion transport and ion-specificity in such channels are only partly understood, especially in mixtures of electrolytes, i.e., under physiological conditions. Electrostatic interactions between the permeating ions and the channel have a significant role in determining both transport and specificity properties. Other factors, such as structural changes in the channels and interactions between ions within the channels, may play a significant, but as yet unknown role. Gramicidin A forms measurable single channels in artificial lipid bilayer membrane. The current-voltage characteristics of gramicidin channels will be studied as a function of concentration of a single electrolyte, in both symmetrical and asymmetrical solutions. These measurements will form the basis for the development of a model for ion tranport in various transmembrane channels. Further experiments will be done to characterize single conductance properties in mixtures of several electrolytes. Special emphasis will be given to whether the properties of channels in mixed electrolytes are predictable from the information observed with single electrolytes. The molecular interactions of gramicidin channels within lipid bilayers will be investigated, as a function of the permeating cation, to see whether these ions can influence channel behavior (structure) on the gross level. The electrostatic interactions of ions within lipid bilayers will be studied using hydrophobic ions absorbed into the membranes as a very simple and tractable model system. Attempts will be made to quantitate ion-ion interactions within transmembrane channels.